New rear end gears -

[ck1984]

Oh great, I dont actually remember that much detail but i think u r right!. according to chev vin decoder , it says my car has 2.29 gears and the weaker THM250c. what i dont understand is why this vin decoder would say i had a 305? i pulled a 305 out of it but i thought it wasnt original due to several mods in the wiring. Shouldnt an olds have the 307?

Doesnt matter all that much right now, since it was such a tight fit going in there i dont think i could pull the transmission without removing entire intake assembly maybe even whole engine and transmission to get at top bolts.
So unless i can only find 3.73 gears and all that extra rpm drives me nuts and sucks fuel like a dragcar, its staying in there until it blows.

besides weaker, whats the actual differences between th350c and thm350 and thm250c? why the 300 rpm difference?

 

[Calgary Rocket]

I have a 2006 F150 truck for winter and 2011 civic for highway driving .
So my 84 Cutlass is just for DD grocery getter or was a going to the gym car everyday. [until yesterday my province re-instated mask and soon Vax passport so i will be working out at home.]
So now its only a weekly summer grocery getter and maybe occasional roadtrip.
It has Th350 mated to 02 5.3LS but still cant peel 1 tire off the line, due to the likely 2.14 gears in rear.

So im looking for 3.08 or maybe 3.42 rear gears. So i may be looking at a 50% more TQ multiplication and faster speed off the line but also 50% more rpm.
what would you recomend?

In my case, I have 4.11 rear gears and posi with a 2004R trans and 2400 stall converter and this is WAY too much gear. It will light up the tires behind the 400+HP aluminum headed 455 up to third gear.
All over the place, but lots of fun. My plan was to do this to keep the wimpy 10 bolt 7 1/2" rear from scattering parts all over the road. LOTS of wheel spin to release the energy but it's time is near.
Looking for a Ford 9" to build over the winter. With a stronger rear end I will lower the rear gear to a 3.23 or 3.43 at the most.

 

[olds307 and 403]

Oh great, I dont actually remember that much detail but i think u r right!. according to chev vin decoder , it says my car has 2.29 gears and the weaker THM250c. what i dont understand is why this vin decoder would say i had a 305? i pulled a 305 out of it but i thought it wasnt original due to several mods in the wiring. Shouldnt an olds have the 307?

Doesnt matter all that much right now, since it was such a tight fit going in there i dont think i could pull the transmission without removing entire intake assembly maybe even whole engine and transmission to get at top bolts.
So unless i can only find 3.73 gears and all that extra rpm drives me nuts and sucks fuel like a dragcar, its staying in there until it blows.

besides weaker, whats the actual differences between th350c and thm350 and thm250c? why the 300 rpm difference?

Other than the 88 model, H/O and 442, all Canadian models had the sbc and non CCC till 86. I believe there is a band vs an extra set of clutches. I killed one behind a 403, the first time out. The lock up converter prevents slippage on the "C" models.

 

[Calgary Rocket]

Other than the 88 model, H/O and 442, all Canadian models had the sbc and non CCC till 86. I believe there is a band vs an extra set of clutches. I killed one behind a 403, the first time out. The lock up converter prevents slippage on the "C" models.

Good notes on the Canadian models. Mine was exactly what you stated. SBC (305) with 2004R and no CCC. Funny, these did retain the OBD connector wired, but not hooked up to anything. (or anything I seen).
I did retain the lock up on the 2004R trans however. My B@M converter can be used lock up or non lockup, but retained the inside trans wiring and added a rocker switch to engage full lock up for highway cruising.
Works well and keeps RPM's at about 2500 in 4th gear at 70MPH (110KPH) with the 4.11 gear.

 

[ck1984]

In my case, I have 4.11 rear gears and posi with a 2004R trans and 2400 stall converter and this is WAY too much gear. It will light up the tires behind the 400+HP aluminum headed 455 up to third gear.
All over the place, but lots of fun. My plan was to do this to keep the wimpy 10 bolt 7 1/2" rear from scattering parts all over the road. LOTS of wheel spin to release the energy but it's time is near.
Looking for a Ford 9" to build over the winter. With a stronger rear end I will lower the rear gear to a 3.23 or 3.43 at the most.

It would be great if i managed to find the sweet spot in gear ratio where it can light up both wheels momentarily then take off.
Right now if i believe the Vin; I have a 2.29 rear gear with Thm250 transmission. Off the line it wont even Chirp street tires on dry clean pavement.
turning a dusty corner and going full throttle will spin 1 tire for 20-30 ft

with a mostly stock truck Ls pushing about 300 hp at crank and mated to the weaker THm250;
whats highest numerical non posi do you think i could go w/o making it into a ONE TIRE FRIER?
whats the highest numerical gear with Posi i could run and be able to just spin both tires a lil and then take off?

 

[Calgary Rocket]

I would think maybe try something around 3.23 or 3.42 max. It is a LS1 correct? These motors have pretty good torque (even the truck models) so those gears should make a huge improvement.
Before my 455 swap, the rear end gears and carrier (posi added) installed, the bone stock SBC 305 put out maybe 150HP ? I could do brake torque burnouts easy with the 4.11's.

 

[olds307 and 403]

If you put a tune on it, your TH250C days are numbered. A 3.08 is as I as I would consider with a 3 spd, especially without a lockup converter. I say a Trutrac posi, is there even an aftermarket 3.08 for the 7.5"? My 70S with a 225/70R14 tire, 2.78 gears with a non lock up TH350 was 2350 rpm at 60 mph. That was about the max I was comfortable with. With the 2004R and the planned 3.90 gears, it will run 350 rpm lower at 60 mph.

 

[ck1984]

I would think maybe try something around 3.23 or 3.42 max. It is a LS1 correct? These motors have pretty good torque (even the truck models) so those gears should make a huge improvement.
Before my 455 swap, the rear end gears and carrier (posi added) installed, the bone stock SBC 305 put out maybe 150HP ? I could do brake torque burnouts easy with the 4.11's.

I this is called an LM7 5.3 LS from 2002 avalanche which is 2000 lbs heavier than my cutlass so it should be tuned for pretty good low end TQ

although it may need a tweaking of the tune cuz it was maybe still is running very rich because of the weight difference or wrong temp setting/sensor, leaky injector, who knows?

I dont really wanna do brake TQ burnouts, i just spent a frustrating afternoon redoing the entire rear drum system. I did eff up the order of brake parts and got double set of new drums but thats besides the point.
to me brake TQing only makes sense if you can just lock the front wheels up, otherwise you are wasting hp overcoming the rear brakes and prematurely wearing them out too.

i could probly rig up my own line lock system by just plumming in a shutoff valve to rear brake lines ;-)

 

[ck1984]

If you put a tune on it, your TH250C days are numbered. A 3.08 is as I as I would consider with a 3 spd, especially without a lockup converter. I say a Trutrac posi, is there even an aftermarket 3.08 for the 7.5"? My 70S with a 225/70R14 tire, 2.78 gears with a non lock up TH350 was 2350 rpm at 60 mph. That was about the max I was comfortable with. With the 2004R and the planned 3.90 gears, it will run 350 rpm lower at 60 mph.

if i get it duno -tuned i will most likely be for regular 87 octane, im guessing 300 crank Hp with larger exhaust and modded intake, unless its no more expensive to get it dyno-tuned for 93 octane premium and will reliably de-tune/retard itself if i keep putting 87 octane in it? in that case maybe 315 HP

the stock cutlass engine was 140 HP & 325TQ. this LS engine stock is 285 HP but about same 325TQ, so knowing its about same Tq and the extra Hp doesnt come online until higher up in the rpm , is it really so dangerous for my weaker THM250C?
isnt it mostly the low rpm TQ that tears trannies apart?

 

[64nailhead]

Yes and no. Yes, evey amount of power upgrade is dangerous to to a THM250C, and no, it's not only low end torque that can hurt the transmission.